Hey guys,
The previous owner of my jeep had installed a sub in the back, but took it out. Since he left the wiring intact I want to install a sub. It looks like there are some audio cable running to the panel under the steering wheel where there may have been an amp at some point. I was wondering if it would be possible to wire the sub directly to the stock Boston amp in the back, so I don't have to buy another amp. Thanks.

No. You'll need a separate amp to drive a sub. The factory BA system doesn't have an output for a sub, so you'll either have to do the Kicker system upgrade or do a LOC like I did in order to add a sub. If there are "cables" strung under the steering wheel, it could have been for about anything. Are they RCAs? Accessory wire? Power wire running to the battery through the firewall?

The easiest way to add a sub to the factory BA system is with a LOC and another amp. I installed my amp in the rear tool tray for a concealed build and left the LOC in behind the trim with the factor BA amp.

No. You'll need a separate amp to drive a sub. The factory BA system doesn't have an output for a sub, so you'll either have to do the Kicker system upgrade or do a LOC like I did in order to add a sub. If there are "cables" strung under the steering wheel, it could have been for about anything. Are they RCAs? Accessory wire? Power wire running to the battery through the firewall?

The easiest way to add a sub to the factory BA system is with a LOC and another amp. I installed my amp in the rear tool tray for a concealed build and left the LOC in behind the trim with the factor BA amp.

They are RCA audio cables. They run from the back of the rear seat to under the wheel. What's a loc?

They are RCA audio cables. They run from the back of the rear seat to under the wheel. What's a loc?

If you've got a factory BA system (including the headunit), then I'm not sure what purpose RCA cables from the front to the rear ever would have served because there are no RCA outs on our systems. This is because in order to use a LOC, or Line [Level] Output Converter, you want to have as much as a full spectrum of sound as possible to tap for your bass or line level output.

The factory BA system has encoded CANBUS signal which leaves the headunit and is decoded at the amplifier in the back trim panel, which then divides out the signals via a built in equalizer. The front speakers are divided into high/mids to the dashboard speakers and lows to the doors. The rear speakers get the full spectrum of sound. Therefore, the sound quality in the rear door speakers is your best bet for the closest to perfect sound qualify (or at least as your headunit interprets the media).

Because the input to the amp is encoded from the headunit, you must tap the output signal from the amp with the LOC. The LOC will be powered (convenient with already existing power wires from the amp OR the 12v DC socket connection next to it) and you'll need to tap the signal going to the rear speakers (see pinouts on WKjeeps). The LOC will have place for output RCA cables, which will then connect to the new amp you'll need for the sub.

As usual, Brent has provided some excellent information. One thing that I would advice against, however, is to use any existing electrical wiring for powering the amplifier that drives the sub woofer. There are several reasons for this, one being it is much safer with a dedicated wiring from the battery to the amp that includes a fuse. If you choose not to run a separate power wires form the battery, you run the risk of affecting other parts of the electrical system should something burn out or short circuit. It is much easier (and cheaper!!) to replace some dedicated wiring rather than replacing OEM wiring harnesses or parts. In addition, existing electrical wires may provide enough voltage for your amp, but the wires may not be able to handle the recommended amperes needed for the amplifier (you can check the requirements for each amplifier by downloading manuals for various amplifiers on their respective manufacturer websites or check with places such as Crutchfield).

I just added a subwoofer to my BA system by using a LOC and the difference is tremendous. I run a Boston G112PS (ported setup) with a smaller 3ooW RMS (bridged) amp and this combination provides more bass than I really need.

As usual, Brent has provided some excellent information. One thing that I would advice against, however, is to use any existing electrical wiring for powering the amplifier that drives the sub woofer. There are several reasons for this, one being it is much safer with a dedicated wiring from the battery to the amp that includes a fuse. If you choose not to run a separate power wires form the battery, you run the risk of affecting other parts of the electrical system should something burn out or short circuit. It is much easier (and cheaper!!) to replace some dedicated wiring rather than replacing OEM wiring harnesses or parts. In addition, existing electrical wires may provide enough voltage for your amp, but the wires may not be able to handle the recommended amperes needed for the amplifier (you can check the requirements for each amplifier by downloading manuals for various amplifiers on their respective manufacturer websites or check with places such as Crutchfield).

I just added a subwoofer to my BA system by using a LOC and the difference is tremendous. I run a Boston G112PS (ported setup) with a smaller 3ooW RMS (bridged) amp and this combination provides more bass than I really need.

Good luck!

Well said WK2007! I didn't mean that he should power the actual amp by the existing wiring, but I can see how what I said can be interpreted to say as much. I powered my LOC via the 12v DC outlet in the back, and used the 12v switched DC outlet in the front as the accessory wire for the "remote switch" on my amp.

TO CLARIFY, emphasizing what WK2007 said, YOU SHOULD NEVER POWER AN AFTERMARKET AMP BY USING EXISTING OEM VEHICLE WIRING HARNESSES OR THE LIKE.

Powering my Fosgate amp is a Fosgate 4ga kit with the power wire running up along the floor trim and through the firewall to the battery. I believe it has a built in-line 100AMP fuse located about 12" from the battery. I ground down and roughed up one of the bolts for the liftgate latch and used that for my amp ground wire.

Also important to note is that if you plan on having a sub/amp with any decent wattage ratings (whether peak or RMS), you should buy your power wires accordingly. My amp pushing up to 1000w RMS is pretty much at the cap of allowable for a 4ga wire.

Also, I never recommend 8ga wire as they typically don't have enough throughput for a decent sub setup. If you cheap out on anything, DON'T cheap out on the wiring kit (some mfgr's use the wire coating when measuring wire thickness, etc).

The previous owner has already done some direct electrical wiring to the rear seats for a sub. Also under the steering wheel I found some bullet connectors. Are these for an amp?

What do you mean by "some direct electrical wiring to the rear seats?" Are we talking 4ga power wire directly from the battery? If not, then it won't be adequate. As for the under the steering wheel wiring, I've never seen anyone locate an amp underneath the steering wheel. There are WAY too many electrical connections under there that would provide a huge amount of interference, not to mention may be sensitive to the heat that an amp would create.

Basically, no one will be able to help you find out what you have without pics to go along with your descriptions.

Ok so I did some digging today, and I found there is a 10 gauge wire for the sub which directly runs to the battery and has a 30 amp fuse. The ground for the sub however is only 18 gauge and connects to a 15 amp factory fuse under the steering wheel. There are 2 wires with bullet connectors that connect to a grey/ yellow and a grey/purple wire near the hood release switch under the steering wheel panel. However the bullet connectors look like someone squished them and rendered them unusable. Pics are attached.

Ok so I did some digging today, and I found there is a 10 gauge wire for the sub which directly runs to the battery and has a 30 amp fuse. The ground for the sub however is only 18 gauge and connects to a 15 amp factory fuse under the steering wheel. There are 2 wires with bullet connectors that connect to a grey/ yellow and a grey/purple wire near the hood release switch under the steering wheel panel. However the bullet connectors look like someone squished them and rendered them unusable. Pics are attached.

Only thing that sucks about that is that that signal has already been scrubbed by the factory amp for low frequency only and you'll still need a LOC to convert it to line level for an amp (unless you have an amp with a speaker level input).

Basically, I'd start my own configuration from scratch and forget what's there. You'll be better off in the end unless you're installing a 50w sub.

Only thing that sucks about that is that that signal has already been scrubbed by the factory amp for low frequency only and you'll still need a LOC to convert it to line level for an amp (unless you have an amp with a speaker level input).

Basically, I'd start my own configuration from scratch and forget what's there. You'll be better off in the end unless you're installing a 50w sub.

Wait I'm confused, if the factory amp has already scrubbed it for low level input, couldn't we just connect that low level to the sub? Shouldn't the sub readily accept said input? Also the 10 gauge is for the sub, not the amp.